A functional round made for a potato cannon (75mm outer diameter, 68mm inner diameter) PVC barrel from the hardware store, the round consists of sabot petals which separate after firing, meaning very high speeds can be achieved for the penetrator.
Fired using a 1m barrel it achieved 200+km/h, but higher is definitely possible as I was firing in a headwind, just try not to remove your fingers while trying.
If necessary, it can be scaled up to any diameter above 68mm, not sure about scaling down as the fins get quite thin when scaling down, the fit is also very exact so some degree of dimensional accuracy is expected for the print.
I strongly recommend PLA+ or stronger for the sabot petals (otherwise they might not survive the initial launch and/or impact after falling down)
The sabot petals can be quite hard to print at the top transition which might result in some errors, but as long as the errors aren't major and it fits down the barrel it is mostly fine.
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The author marked this model as their own original creation.